1. Field of the Invention
The present invention is directed generally to torsional vibration damping arrangements, preferably for the drivetrain of a vehicle, and particularly to torsional vibration damping arrangements with flexible restoring elements alternately preloaded in different directions.
2. Detailed Description of the Prior Art
Numerous concepts are known for damping vibrations, particularly torsional vibrations, which are caused, for example, by rotating components (e.g., a crankshaft) in a motor vehicle. Torsional vibration dampers can be employed alternatively or in addition to balance shafts. Torsional vibration dampers of this kind generally comprise damping masses or deflection masses, and unwanted torsional vibrations can be damped by the mass inertia of these damping masses or deflection masses. A known torque-transmitting torsional vibration damping concept for decoupling the flywheel mass system of the engine from the transmission and drivetrain, for example, is, e.g., the dual mass flywheel with a primary flywheel mass, a secondary flywheel mass and a torsional vibration damping arrangement mounted therebetween.
DE 10 2010 053 542 A1 discloses a torsional vibration damping arrangement or vibration absorber in which deflection mass pendulum units comprise a deflection mass arranged annularly around a carrier and is supported in circumferential direction with respect to the carrier by a plurality of elastically deformable restoring elements (e.g., leaf springs) which are secured thereto and extend radially inward. Provided in the carrier are radially displaceable flyweights or supporting elements at which the radially inwardly extending restoring elements can be supported in circumferential direction at respective carrier supporting regions or force application points. The supporting elements are preloaded radially inward into a basic position by preloading springs associated with these supporting elements and which are supported at the deflection mass. When there is little or no centrifugal force load, the flyweights or supporting elements are held in the basic position under preloading. As the rotational speed increases, the supporting elements shift radially outward as a result of centrifugal force as the compression of the preloading springs increases so that the carrier supporting regions at which the restoring elements extending radially inward from the deflection mass can be supported are displaced radially outward. This alters the free length of the restoring elements that is available for deflection between the connection thereof to the deflection mass and the respective carrier supporting regions in which they are supported via the supporting elements in circumferential direction with respect to the carrier. Accordingly, this variation of the free length also influences the effective pendulum length, shortening of which results in an increase in the natural frequency of the deflection mass pendulum units. As a result, the stiffness and therefore also the natural frequency of the deflection mass pendulum units is variable in a speed-dependent manner such that as the rotational speed increases the stiffness and therefore also the natural frequency of the torsional vibration damping arrangement increases. This is an attempt to achieve a speed adaptation of the deflection mass pendulum units to a vibration excitation order.
Known torsional vibration damping arrangements have an adjusting system that detunes the natural frequency of the torsional vibration damping arrangement or vibration absorber depending upon the speed in order to selectively cancel a vibration excitation order over a wide speed range. The adjusting system preferably comprises a plurality of flyweights or supporting elements which are distributed symmetrically around the circumference of the carrier to minimize unbalance and which are acted upon by a centrifugal force at speed. Further, the adjusting system comprises at least one restoring element or an adjusting spring that exerts a restoring force radially inward on the flyweight. The centrifugal force of the flyweights and the restoring forces of the springs are adapted to one another such that a desired position of the flyweight is achieved depending on current speed (order tracking). The position of a flyweight determines the force application point or oscillating point at a restoring element (e.g., flexible spring or vibration absorber spring) and accordingly directly influences the stiffness and, therefore, the natural frequency of the vibration absorber. The stiffness characteristic of the vibration absorber can be influenced by circumferential play (i.e., play in circumferential direction) between the restoring element and force application point or oscillating point.